Whatever tire you choose, compare it's load capacity rating to the actual weight of your TT. You want at least 15% reserve load capacity and more is better. More reserve capacity reduces the chance of a tire failure. We have 30% on ours by upgrading one load range higher than the factory OEM LRC. The new Endurance are a good bet and have one load range higher in the equivalent size of an existing tire.
As for misc. parts, dealers can be quite expensive. You might try a local independent RV repair/parts shop if there is one. There are quite a few RV vendors online that can have good prices if you know exactly what to look for. CW can be the most expensive (and usually is). Ebay and Amazon can also be good. You can save a LOT by doing some due diligence online.